1. Field of the Invention
The present invention relates to a forging apparatus for forming various kinds of metallic parts, and more particularly, to improvement in a full-enclosed die forging apparatus.
2. Description of the Related Art
A full-enclosed die forging apparatus is well known in which a cavity is formed by an enclosed pair of a stationary die and a movable die that moves toward and away from the stationary die, a punch is plunged into the cavity toward the stationary die to form a material into such a workpiece of a predetermined configuration as a gear and the workpiece is ejected by a knockout system.
Generally, the knockout system is arranged on the side of the stationary die to, after plunging the punch into the stationary die, make the punch move away from the stationary die, as well as pushing and ejecting the material pressed into the stationary die by a knockout pin. In some of forging apparatus of this kind, a material has its one end pressed at the side of the movable die. In this case, since one end of the material will be pressed also into the movable die, the knockout system is arranged on the side of the movable die to push off the material from the movable die by the knockout pin as disclosed in Japanese Utility Model Laid-Open No. 15844/1994.
For forming a workpiece having concavities on its opposite end surfaces or projections on its peripheral surface by a full-enclosed die forging apparatus of this kind, the punches should be plunged into the cavity from the opposite sides, the stationary die side and the movable die side. In this case, however, designing the apparatus to make both the punches move results in having a very complicated structure.
On the other hand, in a case where with one punch fixedly plunged into the cavity by a predetermined length, plunging the other punch into the cavity to form concavities on the opposite ends of a material or projections on its peripheral surface within the cavity of the pair of dies causes a problem that a workpiece cannot be forged satisfactorily because the material of the workpiece may be pressed only from the side of the other punch to make the material flow insufficient in the cavity, as well as making the flow remarkably uneven on the opposite ends of the material.
Under these circumstances, put into practice is such a forging apparatus as shown in FIG. 27, in which with a material Z held at the center of a cavity X by a pair of punches Y1 and Y2, one punch Y2 is moved toward the other punch Y1 by a predetermined length (L), while the cavity X itself is also moved by, for example, half the predetermined length (L), thereby equally pressing the material Z from its opposite ends by the pair of punches Y1 and Y2. Among apparatuses adopting such a differential mechanism are those disclosed in Japanese Patent Publication No. 39711/1991 and No. 85955/1994.
These forging apparatuses employing the differential mechanism are all provided with a pair of dies, an upper die and a lower die which are allowed to move toward and away from each other, a pair of cylinders, an upper cylinder and a lower cylinder which respectively force the upper die and the lower die to a direction which makes them closed, and a pair of punches, an upper punch and a lower punch which pass through these dies, respectively. The apparatus is further provided with a differential mechanism for, with the lower punch fixed and the upper punch mounted to a slide which supports the upper die, bringing down the upper and lower dies while maintaining their closed state according to a fall of the upper punch integrated with the slide and at a speed lower than the moving speed of the slide.
According to the mechanism, with a material supplied to the pair of dies, the upper and the lower dies are closed by the respective cylinders to form a closed cavity housing the material. At this state, when the slide moves downward, the cavity will move downward through the differential mechanism, so that, while the lower punch plunges into the cavity from below, the upper punch relatively plunges into the cavity from above at a speed higher than the moving-down speed of the cavity. Therefore, the material in the cavity is approximately equally pressed from above and below to form a workpiece satisfactorily.
However, any of the above-described differential-type full-enclosed die forging apparatuses requires, in addition to a driving means for driving the slide to move up and down, a pair of cylinders for closing the upper and the lower dies and a differential mechanism for bringing down the closed pair of dies according to the moving-down of the slide and at a speed lower than the moving speed of the slide. Furthermore, the cylinders and the slide should be driven in the apparatus. These factors make structure of the apparatus be complicated and be increased in scale, as well as making its operation complicated. Therefore, it is difficult to apply the apparatuses disclosed in the literature as one station of a multi-stage forging apparatus which has a plurality of forging stations working synchronously with each other.